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fs: add may_copy_tree()

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Add a helper that verifies whether a caller may copy a given mount tree.

Link: https://lore.kernel.org/r/20250221-brauner-open_tree-v1-5-dbcfcb98c676@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-02-21 14:13:04 +01:00
parent b73ec10a45
commit 9ed72af4e2
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GPG Key ID: 91C61BC06578DCA2
1 changed files with 37 additions and 7 deletions
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44
fs/namespace.c
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@ -2808,6 +2808,41 @@ static int do_change_type(struct path *path, int ms_flags)
return err;
}
/* may_copy_tree() - check if a mount tree can be copied
* @path: path to the mount tree to be copied
*
* This helper checks if the caller may copy the mount tree starting
* from @path->mnt. The caller may copy the mount tree under the
* following circumstances:
*
* (1) The caller is located in the mount namespace of the mount tree.
* This also implies that the mount does not belong to an anonymous
* mount namespace.
* (2) The caller tries to copy an nfs mount referring to a mount
* namespace, i.e., the caller is trying to copy a mount namespace
* entry from nsfs.
* (3) The caller tries to copy a pidfs mount referring to a pidfd.
*
* Returns true if the mount tree can be copied, false otherwise.
*/
static inline bool may_copy_tree(struct path *path)
{
struct mount *mnt = real_mount(path->mnt);
const struct dentry_operations *d_op;
if (check_mnt(mnt))
return true;
d_op = path->dentry->d_op;
if (d_op == &ns_dentry_operations)
return true;
if (d_op == &pidfs_dentry_operations)
return true;
return false;
}
static struct mount *__do_loopback(struct path *old_path, int recurse)
{
struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
@ -2815,13 +2850,8 @@ static struct mount *__do_loopback(struct path *old_path, int recurse)
if (IS_MNT_UNBINDABLE(old))
return mnt;
if (!check_mnt(old)) {
const struct dentry_operations *d_op = old_path->dentry->d_op;
if (d_op != &ns_dentry_operations &&
d_op != &pidfs_dentry_operations)
return mnt;
}
if (!may_copy_tree(old_path))
return mnt;
if (!recurse && has_locked_children(old, old_path->dentry))
return mnt;